Stabilized methylenebis-(phenyl isocyanate) compositions



United States Patent 3,394,165 STABILIZED METHYLENEBIS-(PHENYLISQCYANATE) COMPGSITIONS Thomas R. McClelian, Madison, and Richard A.Kolakowski, North Branford, Conn., assignors to The Upjohn Company,Kalamazoo, Mich, a corporation of Delaware No Drawing. Filed Oct. 24,1965, Ser. No. 505,059 6 Claims. (Cl. 260453) This invention relates tonovel isocyanate containing compositions and to processes for theirpreparation and is more particularly concerned with novel, storagestable, compositions derived from methylenebis(phenyl isocyanate), withprocesses for their preparation, and with polyurethanes derivedtherefrom.

One of the diisocyanates commonly used in the preparation of bothcellular and non-cellular polyurethanes is methylenebis(phenylisocyanate). This material is available commercially either insubstantially pure form or in admixture with related polyisocyanateshaving higher functionality. The latter mixtures are generally producedby phosgenation of a mixture of polyamines produced by acid condensationof formaldehyde and aniline; see, for example, US. Patents 2,683,730,2,950,263, and 3,012,008. Such mixed products containingmethylenebis(phenyl isocyanate) are normally liquids at temperatures of20 C. or higher. They therefore present no difiiculties in handling ordispensing through conventional foam and elastomer formulation mixingmachines.

Substantially pure methylenebis(phenyl isocyanate), on the other hand,presents a problem in that it is normally a solid at room temperature(circa 25 C.) having a melting point of the order of 35 to 42 C. Thismaterial has, therefore, to be melted and maintained in a molten statein order that it can be transferred by piping and pumping arrangementsnormally employed in the preparation of polyurethanes.

By substantially pure methylenebis(phenyl isocyanate), as the term isemployed throughout this specification and claims, is meantmethylenebis(phenyl isocyanate) substantially free from, i.e. containingless than about by weight, of polyisocyanates of higher functionalitywhich are normally produced in the preparation of the crude material.The purified form of methylene-bis(phenyl isocyanate) is generallyprepared by distillation of a crude mixture containing the productobtained by phosgenation of the corresponding mixed polyamine asdiscussed above. The product so obtained normally contains approximately90% of 4,4-methylenebis(phenyl isocyanate) and about of thecorresponding 2,4'-isomer and has a melting point of the order of about37 to 41 C. It is to be understood however that the process andcompositions of the invention are not limited to the use of a producthaving this particular proportion of isomers but can be applied to anymethylenebis(phenyl isocyanate) product, including the individual pure4,4'- and 2,4'-isomers, which is substantially free from polyisocyanatesof higher functionality.

It is an object of the invention to convert a methylenebis(phenylisocyanate) which is normally solid at room temperature (i.e.approximately 25 C.), to a storage stable liquid product which issuitable for transfer as a liquid using conventional procedures andapparatus for the preparation of polyurethanes. It is a further objectof the invention to provide a liquid isocyanate composition which can beused in the preparation of all types of polyurethanes for whichunmodified methylenebis(phenyl isocyanate) is currently employed.

These and other objects of the invention are accomplished by means ofthe process of the invention. The latter represents a process forproducing an isocyanate composition which is a stable liquid attemperatures of above about 15 C., which process comprises heating amethylenebis (phenyl isocyanate) which is normally solid at about 15 C.with from about 2% to about 10% by weight ofN,N-di(2-hydroxypropyl)aniline in the presence of a trace of phosphoricacid at a temperature of about 40 C. to about 110 C.

It has been suggested previously that a polyisocyanate such asmethylenebis(phenyl isocyanate) can be reacted with polyols to formeither isocyanate-terminated or hydroxy-terminated prepolymers dependingon the relative proportions of isocyanate and polyol. The prepolymer soformed is then reacted with further polyol, in the case of isocyanateterminated prepolymers, or further isocyamate in the case of hydroxyterminated prepolymers, to obtain the final desired polyurethane. Theprepolymers formed as intermediates in this process are, generallyspeaking, of relatively high molecular weight and viscosity and theproperties, both physical and chemical, of the prepolymer aresignificantly different from those of the starting isocyanate by reasonof the introduction of a plurality of recurring urethane groups in themolecule of the prepolymer.

The treatment to which the starting methylenebis (phenyl isocyanate) issubjected in the process of the present invention is clearlydistinguished from this prior art procedure involving the preparation ofa prepolymer. Thus, the diisocyanate which is subjected to the processof the invention is not changed significantly in physical or chemicalproperties. The material obtained by the process of the invention stillhas an isocyanate equivalent very close to that of the starting materialand it behaves in all respects in substantially the same manner as thestarting diisocyanate. This is a very important consideration in anytreatment which is undertaken to render the normally solid isocyanateliquid at operating temperatures- The process of the invention iscarried out simply by bringing together the starting diisocyanate andthe N,N- di(2-hydroxypropyl)aniline in any desired manner. Theproportion of N,N-di(2-hydroxypropyl)aniline employed is advantageouslyWithin the range of about 2 to about 10% by weight of isocyanate and ispreferably of the order of 4% to 6% by weight of the diisocyanate.

The two reactants are brought together in the presence of phosphoricacid the latter being employed in an amount in the range of about 0.001to about 0.1% by weight based on the isocyanate. The phosphoric acid maybe employed in the reaction in any suitable form or concentration. Forexample, the appropriate amount of or 115% commercial grades ofphosphoric acid can be employed. The exact form in which the phosphoricacid is employed is not critical but the presence of phosphoric acid inthe reaction mixture is a critical feature of the process of theinvention. In a preferred embodiment the phosphoric acid is added to themixture of isocyanate and N,N-di(2-hydroxypropyl)aniline prior to theheating step of the process but, in a less preferred embodiment, thephosphoric acid is added to the mixture after the heating step has beencarried out as described below.

The mixture of reactants is heated at a temperature within the range ofabout 40 C. to about C. until a homogeneous clear liquid is obtained.Generally speaking it is only necessary to heat the mixture for a fewminutes until this point is reached. The resulting product is thenallowed to cool to ambient temperature and it is found that the productso obtained can be stored indefinitely at temperatures as long as 15 C.without showing any signs of solidification.

In certain cases a small amount of a very fine sediment is precipitatedin the reaction product after standing for a prolonged period. Prior tousage the clear supernatant layer can be decanted from this small amountof sediment or the sediment can be removed by other conventionalprocedures such as filtration, centrifuging or the like.

The storage stable liquid isocyanate compositions obtained according tothe invention can be used for all purposes for which the originalunmodified methylenebis (phenyl isocyanate) can be used. Thus theisocyanate compositions of the invention can be used in the preparationof a variety of polyurethanes, both cellular and noncellular, which arepresently prepared using unmodified rnethylenebis(phenyl isocyanate).Such polyurethanes include flexible, semi-rigid, and rigid foams,elastomers including fibres and filaments, sealants, supported andunsupported film's, and the like.

Methods for preparing these various compositions are well-known in theart; see, for example, Saunders et al. Polyurethanes, Chemistry andTechnology, Part 11, interscience Publishers, New York (1962). Ingeneral the physical properties of the polyurethane compositionsprepared from the isocyanate compositions of the invention are at leastas good as the properties of the corresponding compositions obtainedusing unmodified methylene'bis(phenyl isocyanate).

The following example describes the manner and process of making andusing the invention and sets forth the best mode contemplated by theinventors of carrying out the invention but is not to be construed aslimiting.

Example The methylenebis(phenyl isocyanate) employed as startingmaterial had a meltin point of 37 to 41 C. and was found by vapour phasechromatography to contain 90% by weight of 4,4'-methylenebis(phenylisocyanate) and by Weight of the corresponding 2,4'-isoiner. Thismaterial was obtained by distillation of a mixture of polyisocyanatescontaining approximately 50% of methylenebis(phenyl isocyanate) producedby phosgenation of -a mixture of polyarnines which latter was obtainedby condensation of aniline and formaldehyde in the presence ofhydrochloric acid.

A total of 206.5 g. of the above methylenebis(phenyl isocyanate) washeated to 90 C. under a pressure of 12 mm. of mercury. A mixture of 1drop (.05 g.) of 85% phosphoric acid and 52 g. ofN,N-di-(2-hydroxypropyl)- aniline was heated to 90 to 100 C. withthorough mixing and 15.6 g. of the mixture so obtained was added withstirring to the above methylenebis(phenyl isocyanate). The resultingmixture was heated with stirring at 110 C. and maintained at thistemperature for 10 minutes before cooling to room temperature (circaC.). The product so obtained was allowed to stand at room temperatureovernight and was then filtered to remove a small quantity of solidwhich had separated. The clear blue liquid filtrate was maintained in astoppered bottle at ambient temperatures (varying from about 16 C. toabout C.) for 3 months without showing any signs of solidification.

We claim:

1. An isocyanate composition which is a storage stable liquid attemperatures above about 15 C., which composition comprises the productobtained by heating a methylenebis(phenyl isocyanate) which is normallysolid at about 15 C. with from about 2% to about 10% by weight of ll,N-di(2-hydroxypropyl)aniline in the presence of from about 0.001% toabout 0.1% by weight, based on isocyanate, of phosphoric acid at atemperature of about 40 C. to about 110 C.

2. An isocyanate composition which i a storage stable liquid attemperatures of about 15 C. which composition comprises the productobtained by heating a mixture containing approximately by weight of4,4'-methylenebis(phenyl isocyanate) and approximately 10% by weight or"2,4'-methylenebis(phenyl isocyanate) with from about 4% to about 6% byweight of N,N-di(2-hydroxypropyl)aniline in the presence of from about0.001% to about 0.1% by weight, based on isocyanate, of phosphoric acidat a temperature of about 40 C. to about C.

3. A process for producing an isocyanate composition which is a stableliquid at temperatures above about 15 C. which comprises heating amcthylenebis(phenyl isocyanate) which is normally solid at about 15 C.with from about 2% to about 10% by weight ofN,N-di(2-hydroxypropyl)aniline in the presence of from about 0.001% toabout 0.1% by weight, based on isocyanate, of phosphoric acid at atemperature of about 40 C. to about 4. The process of claim 3 whereinthe methylenebis (phenyl isocyanate) contains approximately 90% byweight of 4,4-methylenebis(phenyl isocyanate) and approximately 10% byweight of 2,4'-methylenebis(phenyl isocyanate 5. A process for producingan isocyanate composition which is a stable liquid at temperatures aboveabout 15 C. which comprises heating a methylenebis(phenyl isocyanate)which is normally solid at about 15 C. with from about 4% to about 6% byweight of N,N-di(2-hydroxypropyl)aniline in the presence of from about0.001% to about 0.1% by weight, based on isocyanate, of phophoric acidat a temperature of about 40 C. to about 110 C.

6. The process of claim 5 wherein the methylenebis (phenyl isocyanate)contains approximately 90% by weight of 4,4-methylenebis(phenylisocyanate) and approximately 10% by weight of 2,4'-methylenebis(phenylisocyanate).

References Cited UNITED STATES PATENTS 2,692,874 10/1954 Langerak260-775 2,999,106 9/1961 Prosser et a1 260453 3,012,008 12/1961 Lister260-453 XR 3,179,625 4/1965 Ehrhart 26075 CHARLES B. PARKER, PrimaryExaminer.

D. H. TORRENCE, Assistant Examiner.

1. AN ISOCYANATE COMPOSITION WHICH IS A STORAGE STABLE LIQUID ATTEMPERATURES ABOVE ABOUT 15*C, WHICH COMPOSITION COMPRISES THE PRODUCTOBTAINED BY HEATING A METHYLENEBIS(PHYNYL ISOCYANATE) WICHI IS NORMALLYSOLID AT ABOUT 15*C. WITH FROM ABOUT 2% TO ABOUT 10% BY WEIGHT OFN,N-DI(2-HYDROXYPROPYL)ANILINE IN THE PRESENCE OF FROM ABOUT 0.001% TOABOUT 0.1% BY WEIGHT, BASED ON ISOCYANATE, OF PHOSPHORIC ACID AT ATEMPERATURE OF ABOUT 40*C. TO ABOUT 110*C.